MOSS
LANDING, California—Exploring a deep-sea ridge off Northern
California, scientists at the Monterey Bay Aquarium Research Institute
(MBARI) have discovered a unique undersea nursery, where groups of fish
and octopus brood their eggs, like chickens on their nests. This is the
first time that marine biologists have directly observed any deep-sea fish
brooding its eggs. It is also the first time that two different types of
mobile deep-sea animals have been observed brooding together in the same
area. Although the scientists do not know exactly why the animals prefer
this one area, they believe that the nursery represents a new type of
biological “hot spot” (an area of intense biological activity).

MBARI
scientist Jeff Drazen presented these observations last week at the Deep
Sea Biology Symposium in Coos Bay, Oregon. His research is also featured in the
current (August 2003) issue of Biological Bulletin, which shows
photographs of the brooding fish and octopus on its cover.

The
undersea nursery was discovered and documented using MBARI’s remotely
operated vehicle (ROV) Tiburon. Using video tapes from Tiburon
dives, Drazen and colleagues found that each summer, blob sculpin (Psychrolutes
phrictus) and deep-sea octopus (Graneledone sp.) gather
together at the crest of the Gorda Escarpment, off Northern California.

A blob sculpin (Psychrolutes phrictus)
peers over the edge of a boulder at the ROV Tiburon. This fish is guarding its eggs (which you can see in the background) along the Gorda Escarpment, off Northern California. Blob sculpin commonly grow to 60 cm (2 feet) in length. The animals on the rock are brisingid sea stars (with the feathery arms) and sea anemones. Image (c)
2002 MBARI

“The sculpin
nests look like large splotches of purple strewn across the surfaces of
boulders,” says Drazen. “The parent fish is usually resting on the
seafloor near or on top of the eggs. When I first saw this in the video, I
was surprised because no one had ever documented such behavior in a
deep-sea fish before.” Blob sculpin are typically about 60 cm (2 feet)
long and shaped like large, flabby tadpoles. Drazen estimates that some
sculpin nests may contain up to 100,000 eggs. The nursery area lies near the
crest of an undersea rise, almost a mile below the ocean surface.

MBARI geologists first encountered these nursery
areas in August 2000. While performing geological surveys with ROV Tiburon,
they noticed that octopus and blob sculpin were common near certain cold
seeps, where hydrocarbon-rich fluids seep out of the seafloor. When they
returned to the region in 2001, they brought along biologists, who
realized that the octopus were present in unusually large numbers. On one
dive, the ROV also brought up a rock sample which was covered with eggs.
It wasn’t until later, when Drazen watched videotapes of these dives,
that he realized both the fish and the octopus might be brooding eggs.
Intrigued, Drazen organized a third dive in July 2002, to count the
animals and their eggs and to make more observations. The high densities
of animals measured in certain areas convinced Drazen that these nurseries
might qualify as biological hot spots.

Previously
discovered biological hot spots in the deep sea, such as hydrothermal
vents and the tops of seamounts, have been related to geological or
topographic features that cause an increase the availability of food. The
nurseries on the Gorda Escarpment may represent a totally different type
of hot spot, where physical conditions particularly favor the development
of eggs. Drazen is still not sure what aspect of the physical environment
makes this spot so popular for brooding animals.

Three octopus (Graneledone sp.)
brood their eggs on a rock outcrop along the Mendocino Escarpment, offshore of Northern California.
The octopus are in a typical brooding position, with their heads
down and arms curled outward. Their eggs are hidden underneath
their bodies, which are about 16 cm (6 inches) across. Also on the rock are a deep-sea crab and several types of sea
anemones. This photograph suggests some of the abundance and
diversity of marine life found around the undersea nursery areas
along the Gorda Escarpment off Northern California.
Image (c) 2002 MBARI

Whatever the key conditions may
be, Drazen points out that these areas are critical habitat for the species
involved. He and his co-authors are concerned that these undersea nurseries
could be endangered by commercial trawling or long-line fishing.
Such fishing has expanded into the deep sea as near-shore fish stocks have
declined. For this reason, Drazen suggests that reproductive hot spots
such as this might qualify as areas to be protected from fishing.

Finding
one reproductive hot spot may also help scientists discover other such
areas. But as Drazen points out, “Unlike hydrothermal vent and seamount
communities, which persist for generations, reproductive hot spots may be
seasonal and transitory. This makes such sites especially hard to find. We
hope to learn more about why these animals aggregate on the ridge and use
this information to narrow our search for other important nurseries in the
deep sea.”